draft-ietf-curdle-ssh-modp-dh-sha2-05.txt   draft-ietf-curdle-ssh-modp-dh-sha2-06.txt 
Internet Engineering Task Force M. Baushke Internet Engineering Task Force M. Baushke
Internet-Draft Juniper Networks, Inc. Internet-Draft Juniper Networks, Inc.
Updates: 4250, 4253 (if approved) May 8, 2017 Updates: 4250, 4253 (if approved) June 20, 2017
Intended status: Standards Track Intended status: Standards Track
Expires: November 9, 2017 Expires: December 22, 2017
More Modular Exponential (MODP) Diffie-Hellman (DH) Key Exchange (KEX) More Modular Exponential (MODP) Diffie-Hellman (DH) Key Exchange (KEX)
Groups for Secure Shell (SSH) Groups for Secure Shell (SSH)
draft-ietf-curdle-ssh-modp-dh-sha2-05 draft-ietf-curdle-ssh-modp-dh-sha2-06
Abstract Abstract
This document defines added Modular Exponential (MODP) Groups for the This document defines added Modular Exponential (MODP) Groups for the
Secure Shell (SSH) protocol using SHA-2 hashes. This document Secure Shell (SSH) protocol using SHA-2 hashes. This document
updates RFC 4250. This document updates RFC 4253. updates RFC 4250. This document updates RFC 4253.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 9, 2017. This Internet-Draft will expire on December 22, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1. Overview and Rationale 1. Overview and Rationale
Secure Shell (SSH) is a common protocol for secure communication on Secure Shell (SSH) is a common protocol for secure communication on
the Internet. Due to recent security concerns with SHA-1 [RFC6194] the Internet. Due to recent security concerns with SHA-1 [RFC6194]
and with MODP groups with less than 2048 bits [NIST-SP-800-131Ar1] and with MODP groups with less than 2048 bits [NIST-SP-800-131Ar1]
implementer and users request support for larger Diffie Hellman (DH) implementer and users request support for larger Diffie Hellman (DH)
MODP group sizes with data integrity verification using the SHA-2 MODP group sizes with data integrity verification using the SHA-2
family of secure hash algorithms as well as MODP groups providing family of secure hash algorithms as well as MODP groups providing
more security. more security.
The United States Information Assurance Directorate at the National DH primes being adopted by this document are all "safe primes" such
Security Agency has published a FAQ [MFQ-U-OO-815099-15] suggesting that p = 2q + 1 where q is also a prime. New MODP groups are being
both: a) DH groups using less than 3072-bits, and b) the use of SHA-2 introduced starting with the MODP 3072-bit group 15 all use SHA512 as
based hashes less than SHA2-384, are no longer sufficient for the hash algorithm.
transport of Top Secret information. For this reason, the new MODP
groups are being introduced starting with the MODP 3072-bit group 15
are all using SHA2-512 as the hash algorithm.
The DH 2048-bit MODP group 14 is already present in most SSH The DH 2048-bit MODP group 14 is already present in most SSH
implementations and most implementations already have a SHA2-256 implementations and most implementations already have a SHA256
implementation, so diffie-hellman-group14-sha256 is provided as an implementation, so diffie-hellman-group14-sha256 is provided as easy
easy to implement and faster to use key exchange for small embedded to implement.
applications.
It is intended that these new MODP groups with SHA-2 based hashes It is intended that these new MODP groups with SHA-2 based hashes
update the [RFC4253] section 6.4 and [RFC4250] section 4.10 update the [RFC4253] section 6.4 and [RFC4250] section 4.10
standards. standards.
The United States Information Assurance Directorate (IAD) at the
National Security Agency (NSA) has published "Commercial National
Security Algorithm (CNSA) Suite and Quantum Computing Frequently
Asked Questions (FAQ)" [MFQ-U-OO-815099-15] addressed to
organizations that run classified or unclassified national security
systems (NSS) and vendors that build products used in NSS.
This FAQ document indicates that NSS should no longer use:
o ECDH and ECDSA with NIST P-256
o SHA-256
o AES-128
o RSA with 2048-bit keys
o Diffie-Hellman with 2048-bit keys
The FAQ also states that NSS users should select DH groups based upon
well established and validated parameter sets that comply with the
minimum required sizes. Some specific examples include:
o Elliptic Curves are currently restricted to the NIST P-384 group
only for both ECDH and ECDSA, in accordance with existing NIST and
NIAP standards.
o RSA moduli should have a minimum size of 3072 bits (other than the
noted PKI exception), and keys should be generated in accordance
with all relevant NIST standards.
o For Diffie-Hellman use a Diffie-Hellman prime modulus of at least
3072 bits as specified in IETF RFC 3526 [RFC3526] (Groups 15-18).
Although SSH may not always be used to protect Top Secret
communications, this document adopts the use of the DH groups
provided as an example in the FAQ as well as the use of SHA512 rather
than SHA256 for the new DH groups.
[TO BE REMOVED: Please send comments on this draft to [TO BE REMOVED: Please send comments on this draft to
curdle@ietf.org.] curdle@ietf.org.]
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Key Exchange Algorithms 3. Key Exchange Algorithms
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diffie-hellman-group16-sha512 diffie-hellman-group16-sha512
diffie-hellman-group17-sha512 diffie-hellman-group17-sha512
diffie-hellman-group18-sha512 diffie-hellman-group18-sha512
Figure 1 Figure 1
The SHA-2 family of secure hash algorithms are defined in [RFC6234]. The SHA-2 family of secure hash algorithms are defined in [RFC6234].
The method of key exchange used for the name "diffie-hellman- The method of key exchange used for the name "diffie-hellman-
group14-sha256" is the same as that for "diffie-hellman-group14-sha1" group14-sha256" is the same as that for "diffie-hellman-group14-sha1"
except that the SHA2-256 hash algorithm is used. It is recommended except that the SHA256 hash algorithm is used. It is recommended
that diffie-hellman-group14-sha256 SHOULD be supported to smooth the that diffie-hellman-group14-sha256 SHOULD be supported to smooth the
transition to newer group sizes. transition to newer group sizes.
The group15 through group18 names are the same as those specified in The group15 through group18 names are the same as those specified in
[RFC3526] 3072-bit MODP Group 15, 4096-bit MODP Group 16, 6144-bit [RFC3526] 3072-bit MODP Group 15, 4096-bit MODP Group 16, 6144-bit
MODP Group 17, and 8192-bit MODP Group 18. MODP Group 17, and 8192-bit MODP Group 18.
The SHA2-512 algorithm is to be used when "sha512" is specified as a The SHA512 algorithm is to be used when "sha512" is specified as a
part of the key exchange method name. part of the key exchange method name.
4. IANA Considerations 4. IANA Considerations
This document augments the Key Exchange Method Names in [RFC4253] and This document augments the Key Exchange Method Names in [RFC4253] and
[RFC4250]. [RFC4250].
IANA is requested to add to the Key Exchange Method Names algorithm IANA is requested to add to the Key Exchange Method Names algorithm
registry [IANA-KEX] with the following entries: registry [IANA-KEX] with the following entries:
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diffie-hellman-group18-sha512 This Draft diffie-hellman-group18-sha512 This Draft
[TO BE REMOVED: This registration should take place at the following [TO BE REMOVED: This registration should take place at the following
location: <http://www.iana.org/assignments/ssh-parameters/ssh- location: <http://www.iana.org/assignments/ssh-parameters/ssh-
parameters.xhtml#ssh-parameters-16>] parameters.xhtml#ssh-parameters-16>]
5. Security Considerations 5. Security Considerations
The security considerations of [RFC4253] apply to this document. The security considerations of [RFC4253] apply to this document.
The security considerations of [RFC3526] suggest that these MODP The security considerations of [RFC3526] suggest that MODP group14
groups have security strengths given in this table. They are based through group18 have security strengths that range between 110 bits
on [RFC3766] Determining Strengths For Public Keys Used For of security through 310 bits of security. They are based on
Exchanging Symmetric Keys. [RFC3766] Determining Strengths For Public Keys Used For Exchanging
Symmetric Keys. Care should be taken to use sufficient entropy and/
Group modulus security strength estimates (RFC3526) or DRBG algorithms to maximize the true security strength of the key
exchange and ciphers selected.
+--------+----------+---------------------+---------------------+
| Group | Modulus | Strength Estimate 1 | Strength Estimate 2 |
| | +----------+----------+----------+----------+
| | | | exponent | | exponent |
| | | in bits | size | in bits | size |
+--------+----------+----------+----------+----------+----------+
| 14 | 2048-bit | 110 | 220- | 160 | 320- |
| 15 | 3072-bit | 130 | 260- | 210 | 420- |
| 16 | 4096-bit | 150 | 300- | 240 | 480- |
| 17 | 6144-bit | 170 | 340- | 270 | 540- |
| 18 | 8192-bit | 190 | 380- | 310 | 620- |
+--------+----------+---------------------+---------------------+
Figure 2
Using a fixed set of Diffie-Hellman parameters makes them a high Using a fixed set of Diffie-Hellman parameters makes them a high
value target for precomputation. Generating additional sets of value target for pre-computation. Generating additional sets of
primes to be used, or moving to larger values is a mitigation against primes to be used, or moving to larger values is a mitigation against
this issue. Care should be taken to avoid backdoored primes ([SNFS]) this issue.
by using "nothing up my sleve" parameters.
6. References 6. References
6.1. Normative References 6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 5, line 35 skipping to change at page 6, line 13
parameters/ssh-parameters.xhtml#ssh-parameters-16>. parameters/ssh-parameters.xhtml#ssh-parameters-16>.
[MFQ-U-OO-815099-15] [MFQ-U-OO-815099-15]
"National Security Agency/Central Security Service", "CNSA "National Security Agency/Central Security Service", "CNSA
Suite and Quantum Computing FAQ", January 2016, Suite and Quantum Computing FAQ", January 2016,
<https://www.iad.gov/iad/library/ia-guidance/ia-solutions- <https://www.iad.gov/iad/library/ia-guidance/ia-solutions-
for-classified/algorithm-guidance/cnsa-suite-and-quantum- for-classified/algorithm-guidance/cnsa-suite-and-quantum-
computing-faq.cfm>. computing-faq.cfm>.
[NIST-SP-800-131Ar1] [NIST-SP-800-131Ar1]
Barker, and Roginsky, "Transitions: Recommendation for the Barker and Roginsky, "Transitions: Recommendation for the
Transitioning of the Use of Cryptographic Algorithms and Transitioning of the Use of Cryptographic Algorithms and
Key Lengths", NIST Special Publication 800-131A Revision Key Lengths", NIST Special Publication 800-131A Revision
1, November 2015, 1, November 2015,
<http://nvlpubs.nist.gov/nistpubs/SpecialPublications/ <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-131Ar1.pdf>. NIST.SP.800-131Ar1.pdf>.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For [RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86, Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, DOI 10.17487/RFC3766, April 2004, RFC 3766, DOI 10.17487/RFC3766, April 2004,
<http://www.rfc-editor.org/info/rfc3766>. <http://www.rfc-editor.org/info/rfc3766>.
skipping to change at page 6, line 10 skipping to change at page 6, line 35
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<http://www.rfc-editor.org/info/rfc6194>. <http://www.rfc-editor.org/info/rfc6194>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234, (SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011, DOI 10.17487/RFC6234, May 2011,
<http://www.rfc-editor.org/info/rfc6234>. <http://www.rfc-editor.org/info/rfc6234>.
[SNFS] Fried, , Gaudry, , Heninger, , and Thome, "A kilobit
hidden SNFS discrete logarithm computation", 2016,
<http://eprint.iacr.org/2016/961.pdf>.
Author's Address Author's Address
Mark D. Baushke Mark D. Baushke
Juniper Networks, Inc. Juniper Networks, Inc.
1133 Innovation Way 1133 Innovation Way
Sunnyvale, CA 94089-1228 Sunnyvale, CA 94089-1228
US US
Phone: +1 408 745 2952 Phone: +1 408 745 2952
Email: mdb@juniper.net Email: mdb@juniper.net
URI: http://www.juniper.net/ URI: http://www.juniper.net/
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